A great strategy at all levels is to hit most of your shots to specific targets on the court.
If you are playing singles, pick two targets halfway between the middle of the court and the singles sideline, as well as halfway between the service line and baseline. This gives you a good margin for error and will result in making your opponent move to hit their shots.
If you miss these targets, your shot is still likely to be in and can still get your opponent in trouble, especially if you have hit the shot well.
In doubles, move your targets to halfway between the service line and baseline, right on the singles sideline. Again, this gives you a very good margin for error and should help you make a lot of balls while making it difficult on your opponent.
Hit your targets!